Cutting fiber tow into staple fibers and other predetermined lengths of fiber is well-known in those industries where this is done.
One problem generally associated with cutting fiber tow is controlling the cutting in such manner as to achieve a consistent constant length of cut fiber within certain tolerance requirements. Equipment designed to process cut fibers usually is adjusted to operate with regard to particular lengths of cut fiber.
Another problem, also generally well-known, is fusing of the ends of the cut fiber. This can occur during the cutting operation when undue pressure in the cutting apparatus is allowed to build. This undue pressure, and especially in the case of fiber tow made of synthetic materials, causes heat which, as the heat increases, causes some melting of the fiber. Generally, what happens is that the ends of a cut fiber may fuse along with the ends of adjacent cut fibers to form hard clumps that do not process well in those industries attempting to make a saleable product from cut fibers.
U.S. Pat. No. 3,768,355 (Farmer et al . . . 1973), U.S. Pat. No. 3,978,751 (Farmer et al . . . 1976), U.S. Pat. No. 4,369,681 (Van Doorn et al . . . 1983), U.S. Pat. No. 5,060,545 (Keith et al . . . 1991) represent some of the patented structures that disclose inside-out cutter apparatus.
Farmer et al (U.S. Pat. No. 3,768,355), for instance, discloses a rotatable shaft having an axial bore and an inlet passageway at one end of the shaft and the axial bore for receiving a tow band into the apparatus through the inlet passageway and along the axial bore. The axial bore connects to an outlet passageway that is located exteriorly of the rotatable shaft and is spaced axially inwardly from where the tow band first enters the apparatus. The tow band emerges from the axial bore and the outlet passageway along the surface of a radial aperture followed by a radiused incline. The radiused incline extends partially around the periphery of the rotatable shaft and merges with a raised land that extends the remaining distance around the periphery of the rotatable shaft. The raised land is bordered by non-movable side surfaces between which the tow band is confined in its path around the periphery of the rotatable shaft. The tow band wraps around the raised land. The raised land is surrounded by a plurality of spaced knives radially positioned with their cutting edges spaced from and facing the raised land. The patentees emphasize that all surfaces upon which the tow band slides have "suitable, hard-surfaced polished finishes, well-known in the tow guiding art." The tow band, as it commences to wrap around the raised land, is caught by the cutting edges of the knives as the rotatable shaft is rotated, and the tow band as a first layer then becomes "ironed" against the cutting edges. As the rotatable shaft is rotated, successive layers of the tow band form radially inwardly of the first layer. At some point the magnitude of force between the raised land and the knives builds to the point where the tow band is forced through the knives and becomes sheared at the cutting edges into cut staple, which escape easily between the diverging surfaces of the knives to fall into a container or on a conveyor.
An important advantage of an inside-out fiber cutter apparatus over the type that has the cutting edges facing radially outwardly is that the cutting edges in the first can be spaced much closer together so as to cut significantly shorter lengths of fibers than is possible with the other type. Another advantage: since each knife from its cutting edge to its rear edge diverges from an adjacent knife on either side, the cut fiber escapes between adjacent knives more readily than in the type where each knife from its cutting edge to its rear edge necessarily converges toward an adjacent knife on either side, with the result that the cut fibers do not escape so easily.
A disadvantage of an inside-out cutter apparatus is the greater potential for build-up of heat in the area where the fiber tow is confined for cutting. One reason for this, as may be shown by the Farmer et al patent (U.S. Pat. No. 3,768,355), for example, is that the fiber tow becomes confined within an essentially closed chamber, which is defined by the cutting edges of the knives, the raised land around which the tow band wraps, and the side surfaces bordering each side of the raised land. Another reason is due to the friction and subsequent heat generated by the next incoming tow band layer with respect to the tow band layer that is "ironed" against the cutting edges of the knives. To explain: The tow band has a certain diameter or thickness. When the first layer of the tow becomes "ironed" against the sharp edges of the knives, not all of the filaments making up the diameter or thickness of the tow band are engaged against the sharp edges. When the next layer of tow band emerges from the radial aperture along the radiused incline (as looking at FIGS. 3 and 4), the diameter or thickness of that next layer comes into contact with the portion of the thickness of the tow band that is so "ironed." The consequences: a) the incoming tow band at that area will commence to choke, and since the forward movement of the "ironed` layer of tow band relative to the cutting edges has already been arrested by the cutting edges, the rotation of the raised surface will cause the incoming layer to move against and past the "ironed" layer, thus generating frictional heat, and b) there will be a general tendency for folds or waves to be created in some of the filaments making up both the "ironed` layer and the incoming layer that will be pushed ahead of their respective layers. In this latter manner, the cumulative thickness of the two layers will be further increased, adding to the choking effect and hence increasing friction and generating more heat. This cutter apparatus can only be operated at a relatively slow speed as compared to cutters that cut fiber tow from the outside-in. Attempts to run it faster will only exacerbate the heat problem.
The Keith et al patent (U.S. Pat. No. 5,060,545) has nearly the same essential constructional features as the Farmer et al patent described above, except that the hollow shaft does not rotate, and, in turn, a whorl assembly is connected to the shaft. A rotor assembly, which supports the cutters so that their cutting edges face radially inwardly, is arranged to rotate around the whorl assembly on which a groove is formed around its circumference and on which the tow is positioned for subsequent cutting. The tow emerges from the whorl assembly through a tow path opening that extends over an arcuate segment of the whorl assembly and has a curved surface upon which the tow will travel as it proceeds through the tow path opening. The remainder of the circumference of the whorl assembly includes the aforementioned groove for guiding the tow as it is being cut. This patent also mentions another problem that can be associated with inside-out cutters: Heat generated during the cutting of the tow can cause the production of staple fiber of uneven lengths, because the excess heat may cause an undesirable expansion or contraction of the tow during the cutting operation. The patent thus offers as a solution to the heat problem the introduction of a cooling fluid, such as water, through the stationary shaft and the connected whorl assembly.
The Van Doorn et al patent (U.S. Pat. No. 4,369,681) in its discussion of the prior art mentions still another problem associated with inside-out cutters. In the situation where stationary surfaces are used to direct the tow against the blades, this causes friction and heat build-up. The patent mentions that where a number of rollers are used to press the tow against the blades, the tow tends to take a chordal configuration and the layers of tow tend to shift in and out of the cutting edges of the blades. This results in shaving very short segments of tow, thus creating fiber waste in the form of dust. This dust becomes a nuisance for customers when they process it, it wastes tow and adds unusable weight to the bale of fibers. Since the long ends of the resulting "double cut" fiber are shortened, fiber length and uniformity are decreased. The patent also mentions that in the situation where pressure rollers are used in inside-out cutters, there is a tendency to accumulate filaments around the edges of the pressure rollers, thereby requiring periodic removal, hence lower rate of production. Still further, the patent mentions that where small pressure rollers are used, this results in a high impact cutting action due to the sudden convergence of the surface of the rollers and the cutting edges of the blades. This patent offers a solution to these problems by the use of a single pressure roller, which is as nearly as possible equal in diameter to the inside-out diameter described by the cutting edges of the blades. The resulting pressure roller has an outside diameter larger than one-half the inside diameter described by the cutting edges of the blades. The patent also discloses the use of negative air pressure between the working arc of the pressure roller and the blades relative to the atmosphere inside the periphery of the pressure roller so that the fibers tend to be blown away from the surface and edges of the pressure roller. The patentees contend that this causes the fibers to lay properly for cutting against the cutting edges of the blades.
In many of the inside-out fiber tow cutter apparatus known in the art, a fiber tow generally is caused to emerge from the periphery of a cylindrical surface for winding therearound directly opposite an array of spaced knives. In some apparatus, the cylindrical surface is caused to revolve with respect to the array of knives, and in other apparatus the array of knives revolves around the cylindrical surface. The knives in either case are generally equally spaced from and around the cylindrical surface, and their cutting edges face toward the cylindrical surface and are generally parallel with respect to the axis of the cylindrical surface.
As the fiber tow emerges from the periphery of the cylindrical surface, at some point in the rotation of either the cylindrical surface or the array of knives, the cutting edges catch and retain part of the fiber tow of what becomes the first layer of fiber tow around the cylindrical surface. In this manner the knives then serve to pull the fiber tow from its source through the apparatus for cutting into predetermined lengths. The knives initially do not cut completely through a layer of fiber tow because, if they did, the knives would engage the cylindrical surface, scrub and scar it. This would cause dulling or damaging of the cutting edges of the knives and would also result in roughening the cylindrical surface to the extent that it would become unusable because it would also damage the fiber tow before it is cut. Further, if the knives initially were to make a complete cut through the fiber tow, there would no longer be any connection of the knives to the fiber tow so as to continue pulling the fiber tow from its source and through the apparatus.
The knives, as previously mentioned, therefore, engage only a portion of the first layer of fiber tow while successive layers of fiber tow are formed radially inwardly of the first layer. The extent of the engagement of the knives with the fiber tow depends upon the spacing of the cutting edges of the knives from the cylindrical surface and upon the thickness and denier of the fiber tow. The inner successive layer or layers, when formed, press radially outwardly with respect to and against the first layer caught by the cutting edges of the knives. At some point, therefore, again depending upon the thickness and denier of the fiber tow and the number of layers formed around the cylindrical surface, cutting of some of the filaments in the fiber tow will commence and will continue so long as the rotation of either the cylindrical surface or array of knives continues.
In the course of operation of such apparatus, the fiber tow emerging from the periphery of the cylindrical surface is caused to move in engagement with and past the layer held by the array of knives until it in turn is partially caught and retained by the knives. This relative movement of the two layers past and against each other results in a certain amount of friction between the layers and thus causes a generation of heat. Each successive layer of fiber tow formed also becomes wound rather tightly around the cylindrical surface and tends to make it more difficult to rotate the cylindrical surface, if the latter is the rotatable element. If the array of knives is the rotatable element, the resulting increase in radial pressure through the successive layers to the first formed layer tends to make it more difficult to rotate the array of knives. In either case, this is another source of heat generation.
In some apparatus, also, the fiber tow passes initially through either the hollow passageway of a non-rotating shaft or of a rotating shaft and makes nearly a right-angled turn from the hollow passageway and through the periphery of the cylindrical surface. This also causes a generation of heat as the fiber tow is literally dragged over the surfaces of this nearly right-angled turn. In the present invention, the turn from the hollow passageway through the periphery of the cylindrical surface is made more gradual and over a longer arc in an attempt to minimize the generation of heat from this source.
In inside-out fiber tow apparatus of the prior art, the fiber tow is positioned on the cylindrical surface at essentially right angles with respect to the axis of the cylindrical surface and, as mentioned previously, is wound rather tightly around the cylindrical surface. Also, since the fiber tow is so wound at essentially right angles, it tends to interfere with the fiber tow emerging through the periphery of the cylindrical surface, because it passes over the opening in the periphery, causing further friction at that area of emergence and consequent heat generation. In the present invention, by contrast, the emerging fiber tow is positioned at an acute angle with respect to the axis of the cylindrical surface, thus leading the layer of fiber tow away from the area where the fiber tow emerges from the periphery so that there is no interference of an existing formed layer with an emerging layer. The layer that becomes wound around the cylindrical surface at this acute angle will consequently follow a longer path than in the prior art where the layer of fiber tow is wound around the cylindrical surface at essentially right angles with respect to the axis of the cylindrical surface. This layer in the present invention is then caused to move in the opposite direction, resulting in the creation of slack in this layer. In this manner the fiber tow layer then becomes loosely wound around the cylindrical surface. Further, as this layer is caused to move in the opposite direction, it is also moving against and essentially at right angles to the cutting edges of the knives, creating a "sawing action" as it were, thus aiding the cutting of at least some of the filaments making up the thickness of the fiber tow as rotation continues.